Method of extracting potassium salts from potassium-bearing minerals



UNITED STATES PATENT OFFICE.

ARTHUR CHARLES AUDEN, OF WESTMINSTER, LONDON, ENGLAND.

METHOD OF EXTRACTING POTASSIUM SALTS FROM POTASSIUM-BEARING MINERALS.

No Drawing.

To all whom it may concern Be it known that I, ARTHUR -CHARLES ihUDEN, of London, England, a subject of the King of Great Britain, residing at 5 Victoria street, Westminister, London, Eng land, have invented certain new and useful improvements in Methods of Extracting Potassium Salts from Potassium-Bearing Minerals, ofwhich the following is a specification.

It is well-knoavn1that potassium coinpounds'may be extracted from orthoclase feldspar by means of disintegration and treatment with heat when mixed with salt.

In some previous processes particularly British PatentsNos. 16,730 and 21,697 (Rhod-in) only that class of potassium beau ing mineral known as orthoclase feldspar has been used, but by the process hereafter indicated by me silicates of aluminum and potassium such as orthoclase feldspar, pegmatite, mica and micaceous schist, muscovite, china-stone as also some forms of zeolite particularly those found in a basalt matrix and also silicates of iron and potassium such as glauconite may be used.

The first step in the process is to crush the feldspar or. other mineral s0 that it will pass through a half inch to a quarter inch mesh as it is more economical of power to thus divide this process of obtaining a finely divided product intothe two operations of crushing and grinding (milling) thus relieving the mill of the burden of large pieces of material. I then prepare a mixture con taining crushed feldspar 100 parts, slaked lime 56 parts, common salt L0 parts. ()r the mixture may contain pegmatite 100 parts, slaked lime 60 parts, and common salt 4:2 parts; or it may contain china stone 100 parts, slaked lime 52 parts and common salt 48 parts; or mica, micaceous schist, or muscovitc- 100 parts, slaked lime 56 parts. common salt 45 parts; or glauconite 100 parts, slaked lime 50parts, common salt 50 parts. It is also practicable by this process to recover postassium compounds. from leucite and alunite rock, but as this is more economically accomplished as a-by-product in the recovery of alum salts from the said leucite or alunite rock it is not included in this specification. i

--The mixture is then ground in a tube mill or similar machine to a fine powder, 2'. (2.,

Specification of Letters Patent. Patented Ian 23, 192() Application filed November at ue.

Serial No. 341,240.

so that not more than 20 per cent, will be left on an 180x180 mesh, that which is left on the mesh being returned to the mill and re-ground.

The mixture passed through the mesh is then gradually run into a furnace of the ordinary mull'le or inclined retort type where it is subjected to a temperature of 900 1,000-G. for usually about one and a quarter hours. The time the llllXtlll'GlS in the fur- I nace varies according to the nature of the fore only continue the heating for about one and a quarter hours and sieve out such dead lumps as remain. Poking or stirring while in the retort must not be resorted to as this almost invariably leads to (llSCOlO1tt tion of the products and they are consequently spoiled for the purposes of sale. The charge must not be overheated as this produces clinker, and if the mixture formsclinker the extraction of potassium compounds becomes practically impossible and. further, the clinkered particles are so hard that great damage is caused to the grinding surfaces of the mills to which I shall presently refer. Further, tlie'eifect of this retardation of heating is that much less skill is necessary than by previous processes as it is notnecessary again to roast until the mass falls to a powder. It is quite possible with care and skill to roast the charge in the furnace so that no dead lumps as above mentioned are formed but this involves the charge being too long a time in the furnace to be economical in working costs, and also the capital costs of the extra number of furnaces required for a given output is considerably greater than that of the sieving apparatus next hereafter described. The limitation of the period of roasting so that the dead lumps are not all reduced isa special distinguishing feature of my invention.

After withdrawal from the furnace the roasted mixture is placed on the cooling table, or platform, or is passed through a revolving cylinder and is allowed to cool 55 cent.

down, being spread in a thin layer and gently raked When cool enough not to fire the rakes. It is essential that no iron or metal rakes are used, as the result of the action of the heat upon such rakes is to dis- I color the products, the rakes are therefore made of hard beech wood. No cooling must at any time be permitted in the furnace even if the furnace is being stopped, say for the purpose of repairs, as such cooling produces a mass of dead lumps. It wlll be found that the mixture at this stage is largely disintegrated, but there are some dead lumps'formed in its passage through. the furnace, and it is therefore sieved, and

the accumulated residue (not exceeding as before) is re-ground in a second tube mill to the same fineness as that of the previous grinding, this suspension or cutting 20 short of, the roasting and the sieving out of the lumpy residue is commercially preferable, and, by my process of selection by sieving, re-roasting and re grinding of the residue only, theneoessary fineness is obtained at a very much decreased expenditure of fuel and time and wear of the mills.

The. discharge from the sieving gear is then mixed and conveyed to a lixiviating vat or vats where it is thoroughly mixed with clean hot water, i. 6. usually about75 C. un-

til a new mixture is formed of the consistency of thick cream particular care being taken that the mixture is thoroughly mixed and agitated and that no part is allowed to settle in the form of a lump or cake in the bottom of the vat. I

The above is the process when theraw material consists of silicates of aluminum and potassium but where the raw material is silicate of iron and potassium such as glauconitc the procedure is as follows at this point.

The discharge from the sieving gear is mixed and conveyed into a vessel capable of withstanding heat and pressure, 6. 9., an

autoclave, into which high pressure steam and hot water are added and the whole thor oughly mixed and agitate-d, preferably by means of the revolution of the autoclave between trunnions thus saving the glands and stuffing-boxes necessaryfor stirrers and the of 25% of the total amount of heat required,

the balance of being yielded by the steam itself. Dry heating on one hand or boiling on the other both tend to reduce the amount of potash recoverable, and the for 65 men has the additional disadvantage of forming gobs or oysters i. (a, slimy lumps, which prevent the rapid emptying of the vessel and make it very diflicult to keep clean.

From the lixiviating vat or autoclave the creamy mixture is pumped to a filter press but in the case where the raw material is china stone or similar materials, it is permissible to employ a settling and decantation plant through which the slurry is passed pri-orto its being pumped into the filter press in order to relieve the filter press from treating all the material, the said decantation process separating out a proportion of thematerial whichis not worth treating for the extraction .of potassium. compounds which material is passed direct to the kneading machines to be hereafterdescribed. In. all cases it is permissible to use a. vacuum filter in place of-the filter-press but usually it will be found that the press is the more economical to operate, particularly as regards the power absorbed.

The mixture is' then pressed to a certain degree of consistency and is again washed in water, the filter-press being fitted with through-washing apparatus for this purpose, the said water being of a higher temperature than that used in the-lixiviating vats. This increase of temperature is at this stage possible by reason of the filterpress, being a closed vessel, the increased temperature does not involve the loss by steam and vapor such as would occur if the higher temperature water had been used in the open lixiviating vats, and this process is continued until the pressed mixture shows contents of chlorin about equal to 0.25 of sodium chlorid (NaCl) substantially as described in British Patent No. 21,697 of 1911.

The filter-press is at this stage cut off and this point marks the difference of the treatment of the residuals, I will first follow out my process for dealing with the potassium compounds.

The liquor from the filter-press is piped to an evaporator where the solution is concentrated. Particular care'must be taken not to unduly hasten the process of evaporation and the temperatures used must never be extreme or comparatively very great, as if this is done the product tends to be discolored and though its K 0 contents are only slightdy chemically affected, the sale of a discolored product is very difiicult and produces adverse market conditions. In the case where the raw material is silicate of iron and potassium which frequently contains phosphoric acid (P O )-it is advisable to use two evaporators or sets of eva rators entirely separate as units but working in series, in order to eliminate the said hosphoric acid as one evaporator, even of arge capacity, could not accomplish the separation of both the potassium compound and the phosphoric acidso effectively and economically as two smaller evaporators working in series as here described, the potassium compound being obtained as a chlorid and the phosphoric acid as a phosphate. The material. is finally packed in barrels or bags-preferably the formerand it is important that any store should be kept dry and free from any marked changes of temperature.

Secondly I will now follow out the process of preparing cement from the pressed mixture. After the liquor containing the potassium compound has been removed there remains a damp, pressed and nearly solid mixture, which I refer to the press-cake. This press-cake which must not be either too hard or too dry when taken from the filtenpress, is mixed in a kneading or similar machine with lime which is preferably unslaked, but it must .be carefully noted that this unslaked lime must be well ground to practically the same mesh as that first specified (20% residue on 180x180 mesh) and also that considerably less volume of unslaked lime is necded'than if the same be previously slaked, this difference in volume amounting to 25% in the ca-seof very fat limes but from 18% to 20% may be taken as the general average, but the principal reason why I use unslaked lime is that (1) it slakes itself in the kneading machine and mixes with the slurry therein very intimately and very rapidly, thus saving much time as also power and depreciation of the machine, at least half an hours continuous extra worl ing of the machine frequently not producing such an intimacy of mixture. (2) The press-cake contains still a large amount of water and the self-slaking of the unslaked lime creates heat which drives ofl? quite a considerable percentage of thewater in the form. of steam, thus saving fuel and time in the furnace during the second firing about to be described.

With regard to the amount of lime to be added, there are several conditions to be considered, most of such being decided by the market for the various grades of white cement which can be produced, but in decidingthe amount of lime to be added it is necessary to remember that from i5% to 55% of this lime is required as a constituent of the finished product (white cement) and, weighing the lime'before slaking, this means adding from 10 to parts of lime ((7:10) to each 100 parts (by weight) of press'cake as a dry substance, according to the proper" ties, e. 9. hard or soft, desiredin the finished product, and also adjustment must be made according as to whether the British standard or other specification is being worked to. It must be remembered, however, that the more lime that can be added-within of course practical limitsthe less risk of clinkering I and the formation of dead lumps there is;

tioned and the mixing in the machine-is continned until all the constituents of the mass are distributed quite evenly.

When the adjusted mixture has been thoroughly kneaded and mixed, a small percentage of alum, c. e. alum cake, sulfate of aluminum, soda alum, or similar material equal to about 21}% of the dry weight of the adjusted mixture, is added and the kneading and the mixing is continued until a thorough impregnation of the mixture with the alum is obtained, although the mixture of. alum at this stage is not absolutely necessary.

The mixture is now placed in another furnace similar to that already described where it. is heated for about two to two and a half hours, this second heating is a process of peculiar delicacy, the heat beinggradually and increasingly supplied, that is to say,

there must be first applied the lowest temperature snflicient to dry out the moisture from the mixture; and the l1eat,-as.the moisture departs, must be gradually but continuously increased to about 1100 (1., at which temperature the mixture must be treated for at least one hour. -I have found in practice that in frequent cases one and a half hours were necessary, but the exact period varies according to the material treated and the constitution of the mixture. An essential matter at this stage-of the process is that careful provision must be made for the safe and free escape of the steam generated, and to attain this the charge in the furnace must be firmly but not too tightly packed.

If it is too tightly packed the operation of the furnace is retarded and irregular. and the resultant composition is impracticable for commercial purposes and spoiled. if on the other hand the charge is too. loosely packed, pockets occur, gas and steam are retained therein and the whole process is ruined by reason of the irregular treatment of the niaterial.

When properly roasted. the contents of the furnace are discharged on to a cooling bed or platform as before, and, while cooling, are most carefully raked again with beech wood rakes. After cooling, the re sultant mass is again sieved to the mesh required by market conditions. the residue on the sieve which cannot pass must be again ground to attain the necessary fineness. which fineness is the same as that determined by the said market conditions. The product of this second, branch of the process may at this stage of the process be said to have be come white cement. This white cement at this stage, is generally too sensitive and quick setting for market conditions and its usefulness as a commercial product may be impaired, it is therefore almost always necessary to prepare gypsum, finely divided so asto pass through the same mesh as that i used after the final mill discharge, and add from one and a half to two per cent., and well mix the same with the cement.

Thls mixture may be thinly spread on a -floor for about a week and its quality is I greatlyimproved if at the end of that period it ism1xed and turned again in order that Y the particles shall be thoroughly aerated.

'The amount of gypsum to be used varies 'in accordance with the market conditions and the use for which the white cementis desired and the time of aeration varies in accordance with the amount of lime in the y for despatch.

' of such potassium bearing mineral, lime and salt, and the subsequent sieving out and regrindmg of the coarser parts of such roasted -mixture, and the re-treatment of the whole of the re-ground material, by re-roasting, resieving and re-grinding, substantially as de scribed:

2L In'the manufacture of potassium salts from potassium' bearing minerals, .where such potassium-bearing mineral contains silicate of iron and potassium, the-treatment of a mixture, after roasting and sieving as described in claim 1, of the said potassiumbearing mineral, lime and salt, with steam and hot water in a closed vessel, and the agitation of the contents of the said closed vessel, substantially as described.

3. In the manufacture of potassium salts from potassium bearing minerals, the method which consists in roasting a mixture of such'potassiumbearing mineral, lime and salt, subsequently sieving out the coarser parts of such roasted mixture, re-grinding such coarser parts, and then re-treating the whole of the re-ground material by re-roasting, re-sievingand re-grinding. substantially as described.

, 4. In the manufacture of potassium salts from minerals containing silicate of iron and potassium, the method which consists in roasting a mixture of such material, lime and saltQsieving out the .coarser parts of the roasted mixture, re-grinding said coarser parts and treating the whole with steam and hot water in a closed vessel, substantially as described.

5. In the manufacture of potassium salts from minerals containing silicate of iron and potassium, the method which consists in roasting a mixture of such material, lime and salt to a gradually increasing tempera- .ture of about ,ll00 C., sieving out the coarser parts of the roasted mixture, regrindingsaid coarser pants, and treating the whole with steam and hot water in a closed vessel, substantially as described.

6. In the manufacture of potassium salts from potassium-bearing minerals, where such potassium-bearing mineral contains silicate of iron and potassium, the treatment of a mixture after roasting and sieving as described in claim 1, of the said potassiumbearing mineral, lime and salt, with steam and hot water under pressure -in a closed vessel, and the agitation of the contents of the said closed vessel, substantially as deseribed.

7. In the manufacture of potassium salts from minerals containing silicate of iron and potassium, the method which consists in roasting a mixture of such material lime and salt, sieving out the coarser parts of the roasted mixture, re-grinding said coarser parts, and treating the whole with steam and hot water under pressure in a closed vessel, substantially as described.

8. The herein described method of manufacturing white cement, which consists in (a) roasting a mixture of potassium-bearing minerals, lime and salt, (1)) the subsequent sieving out and re-grinding of the coarser parts of suchroasted mixture, (0) the re-treatment of the whole of the reground material by re-roasting, re-sieving and re-grinding, (d) next treating the said roasted material, which has passed through the sieve, with water to wash out the potash, (e) separating 'the wash-water from the solid matter to bring the latter into the form of press cake, mixing lime with this press-cake under stirring and kneading, and (g) then subjecting this last-named mixture to roasting in a furnace, the product after discharge from this last-named furnace being white cement, substantially as described.

9. The herein described method of manufacturing white cement from potassiumbearing minerals where such potassiumbearing minerals contain silicate of iron and potassium, which consists in (a) roasting a mixture of such potassium-bearing minerals, lime and salt, (1)) the subsequent sieving out and re-grinding of the coarser parts of such roasted mixture, (0) the re-treatment of the whole of the re-gmund material by re-roasting, re-sieving and re-grinding. (til) next treating the whole with steam and hot waterin a closed vessel under agitation of the contents of said closed vessel to Wash out the potash and reduce the silicate of iron, (6) separating the Wash Water from the solid matter to bring the latter into-the form of press-cake, mixing lime With this press-cake under stirring and kneading, and (g) then subjecting this last-named mixture to roasting in a furnace, the prod not after discharge from this last-named furnace being White cement, substantially as described.

10, The herein described method of manufacturing White cement from potassiu1n-' bearing minerals Where such potassiumbearing minerals contain silicate of iron and potassium, which consists in mixture of such lime and salt, (I;

(a) roasting a otassium-bearing minerals, the subsequent sieving out tatio'n'of the contents ofsaid closed vessel to Wash out the potash and reduce the silicate of iron, (6) separating the wash-Water from the solid matter to brin the latter into the form of press-cake, (f? mixing lime with this press-cake under stirring and kneading, and then subjecting this lastnamed'inixture to roasting in a furnace, the product after discharge from this lastnamed furnace being White cement, substantially as describe ARTHUR CHARLES AITDEN. 

